Somatostatin receptor subtype 1 is a PDZ ligand for synapse-associated protein 97 and a potential regulator of growth cone dynamics.
We report that somatostatin receptor subtype 1 (sst1) associates in vivo and in vitro with synapse-associated protein SAP) 97, a membrane-associated guanylate kinase homolog implicated as a scaffolding protein in the structural organization of specialized membrane complexes in various tissues, including the CNS. SAP97 and sst1 were coimmuno-precipitated from rodent brain and from transfected human embryonic kidney (HEK) 293 cells, and pull-down experiments demonstrated that the interaction is dependent on the class I PDZ binding motif in sst1 carboxyterminus. Calorimetric titration indicated that the postsynaptic density-95/discs large/zona occludens-1 (PDZ) 2 domain of SAP97 provides the main contribution to the interaction. We noticed substantial sst1 immunoreactivity in differentiating cortical neurons in culture which declined as the cultures matured. The sst1 immunoreactivity extended, together with SAP97 to neuronal growth cones. Somatostatin (1 microM) triggered retraction of the filopodia and lamellipodia in the growth cones. This growth cone collapse was enhanced by overexpression of green fluorescent protein-tagged sst1, whereas sst1 mutant lacking the PDZ binding motif had no effect. These findings suggest a role for somatostatin signaling in the regulation of growth cone stability, which may involve PDZ domain proteins interacting with sst1 and/or other somatostatin receptors. Consistent with a developmental role, sst1 immunoreactivity was present transiently in the developing mouse cortex, peaking at postnatal day 5 and declining thereafter to low levels in the adult cortex.
Cai
C
C
Department of Biological and Environmental Sciences, P.O. Box 56 (Viikinkaari 5), FI-00014 University of Helsinki, Helsinki, Finland.
Li
H
H
Kangasniemi
A
A
Pihlajamaa
T
T
Von Ossowski
L
L
Kerkelä
K
K
Schulz
S
S
Rivera
C
C
Keinänen
K
K
D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D000831:Animals, Newborn; D002478:Cells, Cultured; D002522:Chlorocebus aethiops; D000074288:Discs Large Homolog 1 Protein; D004622:Embryo, Mammalian; D049452:Green Fluorescent Proteins / Q000235:genetics; D020439:Growth Cones / Q000502:physiology*; D006801:Humans; D047468:Immunoprecipitation / Q000379:methods; D008024:Ligands; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008869:Microtubule-Associated Proteins / Q000378:metabolism; D009154:Mutation; D009474:Neurons / Q000166:cytology*; D054731:PDZ Domains / Q000502:physiology*; D016548:Prosencephalon / Q000166:cytology; D017481:Receptors, Somatostatin / Q000235:genetics / Q000378:metabolism*; D014162:Transfection
D048868:Adaptor Proteins, Signal Transducing; C513314:DLG1 protein, human; D000074288:Discs Large Homolog 1 Protein; D008024:Ligands; D008565:Membrane Proteins; D008869:Microtubule-Associated Proteins; C079240:Mtap2 protein, mouse; D017481:Receptors, Somatostatin; C101130:somatostatin receptor type 1; D049452:Green Fluorescent Proteins